Resonant pulse jet combustion heating device



Aug. 16, 1955 B. LAFFERENTZ ETAL 2,715,436

RESONANT PULSE JET COMBUSTION HEATING DEVICE Filed Aug.. 5, 1952 univ 3/ J0 il INVENTORS ...nur

BY @IMM/ gw Y@ ATTO R N EY-S United rates RESNANT PULSE EET (fiviliiUSliN HEATING DEW/'HCE Application August 5, 1952, genial No. 362,728

Claims priority, appiication Germany August 9, 1951 'tlf Elaims. (Ci. 15d-d This invention relates to a heating device which utilizes the operating features of a resonant pulse jet combustion device, that is, a device having a combustion chamber which, with a connected valveless exhaust pipe, forms a resonator that is excited at its natural frequency by periodic detonations of a combustible mixture which occur in the combustion chamber at acoustic frequency.

Resonant pulse jet combustion devices of the type described have heretofore had only limited application to heating installations because previously known forms thereof operate reliably only with relatively expensive high volatile fuels, and for the further reason that the range within which the heat output of such devices can be varied without interrupting operation thereof is quite narrow.

It is proposed, in accordance with the present invention, to provide a resonant pulse jet combustion device which is provided with a firing fuel feed independent of the fuel which is detonated in the combustion chamber. The independently fed firing fuel is introduced into the exhaust pipe of the device under the control of a valve and at such a distance from the combustion chamber that it is not carried back into the combustion chamber of the device even during the vacuum phase of its operation. Since only a small proportion, of the order of 10 to 20%, of the heat output of the improved device need be produced by the combustion that takes place in the resonant pulse jet device itself, it is possible, by varying the amount of independently fed firing fuel, to obtain a heat output that is variable over a wide range, of the order of from 1 to 5, to from 1 to l0, without interfering with or interrupting the continuous resonant operation of the pulse jet device. Further, the invention makes possible the use of relatively inexpensive low volatile fuels even in a resonant pulse jet combustion device having an exhaust pipe of considerably smaller section than its combustion chamber and which is subject to carbon deposit or coking but is highly stable in its resonant operation.

We have found it advantageous to introduce the independently fed firing fuel into the exhaust pipe of the resonant pulse jet combustion device only during the vacuum phase of its operation. With this arrangement, such fuel is sprayed into the fresh air which is drawn into the exhaust pipe behind the return flowing exhaust gas plug and is there subjected to a mechanical and thermal mixing with this air and preparation for combustion. We have also found it advantageous when using as the independently fed firing fuel, high boiling fuels such as fuel oil or Diesel oil, to bring these fuels into heat exchanging relation with the outer wall of the combustion chamber of the resonant pulse jet device in order to preheat such fuels. This procedure also desirably cools the combustion chamber. For this purpose, the independently fed firing fuel, usually mixed with a small amount of air, may be conducted in a spiral duct around the combustion chamber or through the space between the combustion chamber and a surrounding jacket, or by both atent O ZJSAS Patented Aug. 16, 1955 such means. It is usually preferred to propel the independently fed firing fuel from the exhaust pipe of the resonant jet combustion device through an injector which, in addition to the fuel, carries fresh air into the jacket space surrounding the combustion chamber, which space also acts as a silencer. In this way, it is possible to obtain a fuel and air mixture which is so rich in fuel that some low temperature carbonization takes place within the jacket, and this results in a particularly effective chemical preparation of the fuel for combustion. Flashing back of the llame of the firing fuel may be prevented by blowing the fuel tangentially into the jacket space and by providing a narrow exit gap from this space within which the velocity of flow exceeds the speed of propagation of the flame. In order to positively prevent extinguishing of the flame, a hot spot or element may be provided in the wall of the combustion chamber adjacent the point where the independently fed firing fuel leaves the jacket space and is burned.

in describing the invention in detail, reference will be made to the accompanying drawings, in which certain embodiments thereof are illustrated.

In the drawings:

Fig. l is an elevation, partly in section, diagrammatically illustrating a resonant pulse jet combustion device in which independently fed tiring fuel is drawn into the exhaust pipe through a check valve and throttle valve;

Fig. 2 is an elevation similar to Fig. l, diagrammatically illustrating a modification of the invention, in which a preheated fuel and air mixture is propelled and ignited by a resonant pulse jet combustion device;

Fig. 3 is an elevation, partly in section, illustrating a further modification of the invention, in which the ndependently fed firing fuel is mechanically propelled in the exhaust pipe of the pulse jet combustion device and is propelled through a jacket space around the combustion chamber;

Fig. 4 is an enlarged sectional elevation of a portion of the device illustrated in Fig. 3; and

Fig. 5 is a sectional view of the injector connection of ,the device illustrated in Fig. 3.

Referring to the modification illustrated in Fig. 1, the resonant pulse jet combustion device consists essentially of an exhaust pipe 1 directly connected to and extending laterally from a combustion chamber 2. During the vacuum phase of its operation, air is drawn into the combustion chamber through the check valve 3 and inlet duct 5 and fuel is drawn in with such air from the jet 4 of the carburetor 4. The fuel and air mixture is ignited in the inlet duct S by the glow coil 6 at the inner end of the ignition plug 6 and upon ignition detonates, propelling a jet or plug of hot exhaust gases through the exhaust pipe 1 into the fire box 7. The movement of the exhaust gas plug-out of the pipe 1 produces a vacuum phase in the combustion chamber 2 following the detonation phase and as a consequence, a new charge of fuel and air is thereby drawn into the combustion chamber. The described cycle of operations comprising the succeeding detonation and vacuum phases is repeated periodically at an acoustic frequency corresponding to the `natural period of the resonator formed by the combustion chamber 2 and the exhaust pipe 1. This operation of a resonant pulse jet combustion device is explained, for example, in Patent No. 2,644,512. The described arrangement provides means for automatically feeding fuel to support the detonations during each succeeding vacuum phase of operation. The heat output of the resonant pulse jet combustion device thus far described is limited and is variable only within a very narrow range if resonant operation is to be maintained. According to the invention, there is connected to the exhaust pipe 1, near its outer end, a branch tube 3 8, and a check valve illustrated as a spring leaf 9 is provided at the mouth of the tube 8 where it enters the pipe 1. A throttle valve 10 is provided in the tube 8. The jet 11 of a carburetor 11 opens into the tube 8 below the throttle valve 10'. The'carburetor 11` is supplied with the independently fediring fuely from a suitable source. With this arrangement, the independently fed firing fuel is drawn intothe exhaust pipe 1' from the tube 8 only during/'a vacuum phase of the operation of the resonant pulse jet combustion device. In order to increasethe vacuum produced inthe exhaust pipe 1, that pipe may be provided atA its mouth with a stepped attachment'1'2 which retards return ow at this point by the formation of eddies or turbulence inthe flowing gas orv air. The resonant pulse jet combustion device' is started by connecting a small air pump or blower to the pipe 13 to force air int'o the inlety duct 5; The air so introduced draws fuel from the jet 4 and the fuel and air mixture is ignited by the glow coil 6 which is heated by energization of the ignition plug 6. Asl soony as resonant combustion has started, the throttle valve 10 is opened, whereupon the lower volatile firing fuel is drawn into the tube 8 from the jet 11 ofy thecarburetor 11 and is introduced into theY exhaust pipe 1 through the check valve 9. Inthe exhaust pipe 1*, the separately fed tiring fuel is picked up by the oscillating gas column which, during each cycle of operation, first' propels this fuel toward the combustion chamber 2 to about the midpoint of the pipe 1 during the vacuum phase of the cycle, and then, during the ensuing detonation phase, blows the fuel out of the pipe 1 into the tire box 7, where the fuel entrains air to support combustion at the outlet of the exhaust pipe and burns in a flame F. During this process, the tiring fuelmixed with air is thoroughly prepared both mechanically by mixing and thermally by heating, so that when it leaves the exhaust pipe 1, it burns'with a clean blue flame, the heatl output of which may be variably controlled over a wide range by adjustment of the throttle valve 10.

As indicated by the arrow S, representing the' movement thereof, the firing fuel does not move inward into the combustion chamber 2, but is ignited only in the fire box 7. For this reason, combustion of the separately fed'ring fuel does not interfere with the pulsation of the resonant pulse jet combustion device 1, 2 nor does such combustion produce carbon deposits or coking within such device.

In a modified form of the invention illustrated in Fig. 2, the combustion chamber 2 is provided with a jacket 14 that communicates with a jacket tube 15 surrounding the exhaust pipe 1. The mouth of the jacket tube 15 is provided with a constriction 16 and forms an injector with the mouth of the exhaust pipe 1. Following a detonation phase of operation a plug of hot exhaust gas passes thrugh this injector and draws in fresh air through the filter 17 and the jacket space formed by the jacket 14` and tube 15, which air cools the combustion chamber 2 and is thus heated to a few hundred degreesv centigrade. This heated air, with tiring fuel introduced as explained below, is thereafter mixed with the exhaust gases of the resonant pulse jet combustion device at the injector and is blown into the re box 7 by such gases as hereinafter explained.

The independently fed firing fuel flows from a tank 21 through a control valve 20 to a jet 19, which projects into the space 18 between the jacket 14 and the combustion chamber 2. The tank 21 is tightly closed, and super-atmospheric pressure of about 0.5 to l atmosphere is supplied to the head space thereof to force the fuel from the jet 19. The pipe 22 connects the head space of the tank 21 to the exhaust pipe 1 through a check valve 3h provided with a restricted bypass 31. The peak pressures of the periodic detonations of the device are transmitted to the fuel tank head space' through the check valve, while the building up of excessive pressure l in the tank or the persistence of pressure when the device is inactive is prevented.

The amount of air entering through the lter 17 is so small in proportion to the amount of fuel from the jet 19 that the fuel-air mixture in the jacket space 18 is not detonated but is merely heated with a slight low temperature carbonization of the firing fuel. At the mouth of the exhaust pipe 1, this fuel and air mixture that has been drawn to this point by the injector at the end of a detonation phase of operation is drawn back into the exhaust pipe during each succeeding vacuum phase of operation, but only to a point therein short of the combustion chamber 2. The mixture thus drawn in is mixed with the inflowing exhaust gases in the pipe 1, and these exhaust gases, although not materially cooled by `the fuel-air mixture, do not increase the igniting ability of the mixture. Air sucient to support combustion first enters the mixture at the mouth of the jacket tube 15 as the mixture enters the fire box 7, and the prepared firing fuel burns at this point in a clean blue ame F.

A compact and particularly desirable embodiment of the invention is illustrated in Figs. 3 and 4. The combustion chamber 2a is disposed within a jacket 14a around which the exhaust pipe 1a is wound in spiral turns, as shown;

An inlet tube 23 having aninlet mouth in the shape ofa funnel 23a is connected tangentially through the jacket 14a to the jacket space 18a surrounding the combustion chamber 2a. The outlet mouth of the exhaust pipe 1a forms an injector 24 with the inlet mouth 23a of they inlet tube 23.

The relatively low volatile tiring fuel is fed under pressure from the closed tankv21 through the control valve 20 and jet 19a into the exhaust pipe 1a adjacent its' mouth. Fuel feeding pressure is maintainedin the head space of the tank 21 by a pipe 22 connected to the inlet tube 5 of the resonant pulse jet combustion device and provided with a bypassed check valve 30, 31, as in the embodiment of Fig. 2. The fuel entering the exhaust pipe 1a is mechanically and thermally conditioned for combustion therein, asy explained in connection with the modification of Fig. l, and is then blown through the injector 24` and the inlet tube 23 in a tangential course into the circular jacket space 18a between the jacket 14a and the combustion chamber 2a. The fuel thus circu-V lates around the combustion chamber 2a in a spiral path and is thereby further prepared for combustion and finally ows out of the jacket mouth 32 and is injected into the fire box 7, where is entrains and is mixed with more'airI passing through the inlet 7 and burned in a hot clean flame F. r g

In the embodiment of Figs. 3 and 4, it is possible' to maintain such a high speed of ow at the injector 24' that no ignition of the fuel takes place at this point. Igni;

tion within the jacket space 18a is prevented by providingv a narrow annular gap or constriction 25 to maintain a' providing in the end wall of the combustion chamber 2a' adjacent the jacket mouth 32 a small thin walled cup 26 of non-scaling metal, such as stainless steel. This cup is maintained at a red heat during operation of the device and so acts as a hot ignition spot which effectively ignites the fuel-air mixture and keeps it ignited. A ring 27 having radial holes 27 therethrough may be secured around the cup 26 to insure circulation of a small part of the fuel-air mixture into contact with the cup 26.

All of the described embodiments of the invention operate without a blower and are much more simpleT and compact than previously known liquid fuel and fueloil burners. The mechanical feeding of fuel is required only until the resonant pulse jet combustion device' is in proper pulsating operation. The firing fuel is so welll prepared and conditioned mechanically and thermally that relatively heavy oils may be burned without formation of carbon or coking. Extinguishing of the flame is avoided because the exhaust gases of the resonant pulse jet device act as a constant source of ignition.

Due to the low weight of the heating devices of the invention, they are particularly suited for use as portable heating plants, such as eld kitchens, tent heaters and warming installations for construction projects and airports. Since the devices produce excess pressure in the iirebox, they do not require a stack or chimney. The widely variable range of heat output of the improved devices makes them also useful in heat engines, such as hot air engines and steam engines with flash boilers.

We claim:

1. A combustion heating device comprising a resonant pulse jet combustion device including a combustion chamber, an elongated exhaust pipe directly connected to said combustion chamber and forming therewith a resonator, means for automatically feeding fuel and air to said combustion chamber to produce successive detonation phases and intervenino vacuum phases of operation, a jacket spaced from and enclosing at least a portion of the combustion chamber, means for introducing a tiring fuel and air into the space between the jacket and the combustion chamber for preheating, said jacket having an outlet for the discharge of the preheated ring fueland air mixture, and means operatively associated with the outlet of said exhaust pipe for propelling said fuel and air mixture through said jacket and to a zone for combustion.

2. A combustion apparatus according to claim 1 having valve-control means for regulating the amount of firing fuel introduced into the space between said jacket and the combustion chamber.

3. A combustion heating apparatus according to claim 1 in which the exhaust pipe includes a section extending around said jacket.

4. A combustion apparatus according to claim 1 in which the jacket, adjacent the outlet therefrom for the discharge of preheated firing fuel and air, is positioned sutficiently close to the combustion chamber to provide a passageway sulliciently restricted in size as to so increase the speed of the firing fuel and air passing therethrough that flashing back of flame into the space between the jacket and the combustion chamber is prevented.

5. A combustion apparatus according to claim 1 in which the combustion chamber has a portion so positioned that on operation of the pulse jet combustion device it is heated to a temperature sufficiently high to ignite the ring fuel and air, said portion being so positioned that the firing fuel and air passing through the space between the jacket and combustion chamber to the outlet from the jacket is caused to be brought into contact therewith.

6. A combustion apparatus according to claim 5 in which said portion of the combustion chamber includes an inwardly recessed part and a perforated collar surrounding the entrance to the recess of said recessed part.

7. A combustion apparatus according to claim 6 in which said portion of the combustion chamber comprises a cup of non-scaling metal.

8. A combustion apparatus according to claim 1 including an injector means for conducting the firing fuel and air expelled from the space between said jacket and the combustion chamber and for mixing additional air therewith to form a combustible mixture.

9. A combustion apparatus according to claim 1 in which the combustion chamber and the surrounding jacket are circular in cross-section and the means for introducing the tiring fuel and air is so positioned as to cause the tiring fuel and air to be introduced tangentially into the annular space between said jacket and the combustion chamber, whereby said firing fuel and air is caused to How around the combustion chamber within said jacket.

10. A combustion device according to claim 1 having means adjacent said outlet opening of the jacket for supplying additional air to support combustion of the ring fuel.

11. A combustion device according to claim l in which said second named means includes means for introducing the firing fuel into the exhaust pipe, and means for aspirating the air into the mixture of exhaust gases and tiring fuel before it is conducted through said jacket space.

References Cited in the file of this patent UNITED STATES PATENTS 1,273,466 Doble July 23, 1918 1,861,014 Howard May 31, 1932 2,605,608 Barclay Aug. 5, 1952 2,612,748 Tenney et al. Oct. 7, 1952 2,621,718 Krautter et al Dec. 16, 1952 FOREIGN PATENTS 66,519 Great Britain Feb. 13, 1952 

